The right arm represents a positive reaction to PPD (a skin test for tuberculosis protein. The left arm represents a positive reaction to Candida protein. Candida antigen is tested to determine if the individual's immune system is functioning well; a normal immune system demonstrates a positive reaction. Update Date: 07/17/2007Donald Accetta, MD, MPH, President, Allergy & Asthma Care, PC, Taunton, MA. Review provided by VeriMed Healthcare Network.